Coffee roasting weight loss

Coffee always weighs less coming out of the roaster than it did going in. That shrinkage isn't waste to ignore — it's one of the most useful measurements a home roaster has. Weight loss is the closest thing to an objective, repeatable readout of how far a roast actually went, and unlike judging color by eye, your kitchen scale never lies.

Why beans lose weight

Two things happen during a roast. First, the beans give up moisture: green coffee carries roughly 10–12% water, and most of that evaporates during the drying phase. Second, as roasting continues the beans shed organic mass — gases like CO2 and volatile compounds drive off, and chaff flakes away. The longer and hotter the roast, the more mass is lost. That's why weight loss tracks so closely with roast level.

Typical weight loss by roast level

• Light roast: about 11–14%. Dropped soon after first crack, so less mass burns off.
• Medium roast: about 14–17%. The most common range for everyday roasting.
• Dark roast: roughly 17–20%+. Pushed into or past second crack, losing the most mass.

Treat these as guidelines, not laws. The starting moisture of your green coffee, bean density, processing method and your specific roaster all shift the numbers. A high-moisture natural-process bean will read differently than a dry-dense washed one at the same color. What matters is consistency within your setup.

Why it matters for your roasting

Once you know that a particular bean tastes best at, say, 15.5% loss on your roaster, you have a concrete target to hit every time — far more precise than "medium-ish brown." It also acts as a sanity check: an unexpectedly low loss often means the roast was underdeveloped (it'll taste sour), while an unusually high loss warns you it went darker than planned. And practically, weight loss tells you your real yield: 250 g of green at 16% loss gives you about 210 g of roasted coffee to brew with.

Measuring it accurately

Weigh the green beans before charging and the roasted beans after they've cooled. Use the same scale, and let the beans come down to room temperature first since hot beans are still off-gassing. Record both numbers every batch — over time the pattern across beans and roast levels becomes your personal map. RoastLog computes weight-loss % the instant you enter green and roasted weight, and Pro shows your per-bean averages so you can see your true target for each coffee.

Related: Roast levels explained · Development time ratio · RoastLog app